1. Field of the Invention
The present invention relates to an anthracene derivative. Moreover, the present invention relates to a light-emitting material, a material for a light-emitting element, a composition for coating, a light-emitting element, a light-emitting device, and an electronic appliance each of which uses the anthracene derivative.
2. Description of the Related Art
A display device including a light-emitting element (an organic EL element) in which an organic compound is used as a light-emitting substance has been developed rapidly as a next generation display device because it has advantages such as thinness, lightness in weight, high response speed, and low power consumption. Although there have been various obstacles in the development, technique has been improved such that organic EL televisions have become commercially available recently.
In an organic EL element, by voltage applied between a pair of electrodes which have a light-emitting layer interposed therebetween, electrons and holes injected from the electrodes are recombined so that a light-emitting substance is excited, and when the excited state returns to a ground state, light is emitted. The wavelength of light emitted from a light-emitting substance is peculiar to the light-emitting substance; thus, by using different types of organic compounds as light-emitting substances, light-emitting elements which exhibit a variety of wavelengths, i.e., a variety of colors can be obtained.
In the case of a display device which is expected to display images, such as a display panel, at least light of three colors, i.e., red, green, and blue are required in order to reproduce full-color images. To achieve this, for example, there are following methods: a method in which a color filter is used in combination with a light-emitting element that emits light with an emission spectrum in a wide wavelength range, a method in which a color conversion layer is used in combination with a light-emitting element that emits light with the shortest wavelength among the wavelengths of desired colors, and a method in which a light-emitting element that emits light with a desired wavelength is used. Among these three methods, the last one, i.e., a method by which a desired color is directly obtained is preferable because loss in energy is small in this method.
This method is employed in the above-described organic EL televisions which have become commercially available; however, actually, in addition to that method, a color filter is used and a micro cavity structure is further used for a light-emitting element in order to improve color purity. Organic EL televisions having got many advantages are naturally expected to provide high quality images as next generation televisions, and light-emitting elements exhibiting appropriate emission colors are required to live up to the expectation.
Light emitted from a light-emitting substance is peculiar to the substance, as described above. There are many measures to improve the color purity of the organic EL television, which means that it is very difficult to obtain a light-emitting element which exhibits light emission of a favorable color and also satisfies other important requirements of lifetime, power consumption, and the like. In addition, important characteristics of a light-emitting element, such as a lifetime or power consumption, do not necessarily depend on only a substance exhibiting light emission. The characteristics are largely affected also by layers other than a light-emitting layer, an element structure, an affinity between a light-emitting substance and a host, or the like. Therefore, it is true that many kinds of materials are necessary for light-emitting elements in order to further extend this field. In view of this, materials for light-emitting elements which have a variety of molecular structures have been disclosed (for example, Japanese Published Patent Application No. 2007-15933).